In producing oil and gas wells, a tubing string is normally installed in the well extending from the surface into the hole, whether cased or open, downwardly to the production zone of interest. As is known, there may be two or three zones flowing into a well and there may be more than one tubing string in the well, with each tubing string isolated from other tubing strings and typically extending to different production zones. Optimum production of oil and gas from a given well is often dependent on the flow rate of the well which in turn is substantially dependent on the zone or formation pressure. Normally the pressure drops the instant that any flow occurs and to this extent, a measurement of pressure at the well head is not normally reflective of a formation pressure. Formation pressure is best measured at the formation itself; further it is sometimes also helpful to measure other variables at the formation such as temperature.
Typically, formation measurements must be taken over a time period, often ranging as high as twenty-four hours. The typical instrument used for measurement of bottom hole pressure or other bottom hole variables is a clock driven chart mechanism. Of necessity, it is rugged and yet comprises a delicate instrument package. To prevent damage, the mechanism is run into the tubing string and subsequently retrieved with a minimum of banging, jarring, and/or dropping. Moreover, the mechanism is best installed on a device which may be left untended over the requisite time span to avoid excessive personnel charges.
With the foregoing being only exemplary the present invention discloses a tool capable of packing off the tubing string when it is installed. To this end it incorporates an expandable resilient element which includes a slip or collet operated expandable mechanism which locks in place and enables bleeding off of pressure at the time of release of the packoff. Further, since the tubing string is plugged by the tool, there is the likelihood of pressure build up below the tool and hence, there is a means for releasing pressure below the tool.
In addition a plurality of setting or detent means are provided in combination with the isolation means to prevent unwanted dropping or upward movement by the isolation means.